Art of esterification



Patented c 28, 1941 William Beach Pratt, deceased, M

Harri! Pratt, adminlltratrix,

Mass, by Annette Boston, Mass., assignor, to Joseph G. Denny, Jr. v

No Drawing. Applic Serial No. 2 Claims. (01. 260-229) Broadly speaking, this invention relates to esterification with organic acids and anhydrides, or mixtures of the same, particularly to the esterification of cellulose, starch, dextrins and other carbohydrate bodies preferably in their natural or normal state, as individual fibers, granules, fiber aggregates as woven goods, cloth, textiles or twisted or untwisted rovings and yarn, composed wholly or partially of cellulose.

This invention involves novel procedure and compounds used in the formation off valuable products, and especially applicable wherein the original appearance of the fiber or granule ,may or may not be materially modified in appearance by transformation into the corresponding ester form, and whereby the toughness, flexibility and.

elasticity of the esterified carbohydrate in nearly every instance is at least equal to the original body from which the ester has been prepared, especially when the natural carbohydrate is a fiber or filament prior to esterification,

In general, the practice of this invention involves treatment of a single or mixed carboP- hydrate, as normal, natural cellulose, as distinguished from hydrocellulose, hydrated cellulose, oxycellulose, degraded or otherwise modified normal cellulose, or there may be used a mixture of celluloses with other fibrous bodies, said carbohydrate being in the substantially anhydrous condition when catalysts, diluents and/or reactants are contacted therewith, and. initially treat the same with a body or bodies having catalytic functions, dissolved or suspended in a neutral volatile liquid, which liquid may be an ester or susceptible.

to esterification in the carbohydrate esterifying bath, to an ester of the same acid radical as the carbohydrate esterified, yet in the esterified condition is usually substantially a non-solvent, or

' at best a poor solvent of the carbohydrate ester formed.

, catalyst solvent by msne assignments,

ation Assist 8,1940,

or hydroxides, or mixture of similar or dissimilar aliphatic hydroxides with aliphatic oxides, and which are substantially anhydrous when used as or diluent, which comprise in the hydroxide form less than five atoms of carbon, or in the oxide form less than ten carbon atoms,

and which are soluble in or partially miscible with water, and are also capable of esterification in the same bath in which the carbohydrate is being esterified, but which aliphatic ester when formed is a non-solvent or at best a weak solvent of the esterified carbohydrate, thus permitting said carbohydrate to be esterified under normal pressure and tension without appreciable change in physical form or appearance.

Where an aliphatic hydroxide of more than five carbon atoms or the corresponding aliphatic oxide of more than ten carbon atoms are employed hydrate to be esterified, it is preferred to employ natural or normal cellulose in the fibrous state, as linters, fiy, rovings, staple, woven, sheeted or pressed form, as yarn, cloth or'textiles, and from which substantially all atmospheric moisture has been removed at the time the celluloseis initially treated.

If woven'or textile fibers are to be esterified and with little or no observable change in form, structure or appearance during esterification, there may be employed a textile wholly of natural cellulose fibers, or a mixture including mercerized or other treated or modified cellulosic fibers, or

a mixture of cellulosic natural fibers with other fibers containing nitrogen, as wool or silk.

' As catalyst there is employed a body in the liquid or solid state, or a plurality of suitable dissimilar bodies, which are partially or totally soluble in or miscible with an aliphatic hydroxide alone or. admixed with an aliphatic hydroxide, or oxide of lesser carbon content, less satisfactory results have been obtained.

As aliphatic hydroxide, oxide or ester, there may be used methyl alcohol or ethyl alcohol as examples, either alone or admixed together in various proportions, or with a proportion of the corresponding or other oxide, as diethyl oxide,

(ammo, or an alkyl ester of an aliphatic monocarboxylic acid as methyl or ethyl acetates.

Or, there may be used a higher alcohol mixed with a lower one as iso-propyl and methyl alcohol, as example, but it is preferable that the liquid be substantially anhydrous when catalyst is dissolved therein or mixed therewith and the mixture contacted with the carbohydrate.

As catalyst there'may be employed any suitable halogen (except fluorine) oxyacid or anhydride of the same, or mixtures of halogen oxy-acids or anhydrides of same or dissimilar oxygen content, but preferably of relatively high oxygen content, which is or are miscible with or soluble in the above mentioned aliphatic alcohols, others, esters, or mixtures thereof.

As a specific example of relatively high oxygen content," satisfactory results may be obtained by the use of chloric or perchloric acids or their anhydrides chlorine pentoxide, chloric anhydride or chlorine heptoxide (perchloric anhydride), as distinguished from the lower oxyacids, chlorous or hypochlorous, or their respective anhydrides, and less satisfactory efiects result from the use of corresponding oxyacids, containing not less Q than three oxygen atoms, of the halogens bromine with perchloric acid, in conjunction with a relatively minor'proportion of other oxyacid, relatively, high in oxygen as sulfuric acid or phosphoric acid, the selection of most suitable halogen oxyacid catalyst or mixture thereof in esterifying a particular carbohydrate body, depending in a, measure upon the nature, source, form and other characteristics'of the carbohydrate initially used, and the form and physical properties desired in the finished esterified product.

One preferred method of practice of this invention taking the carbohydrate group as a whole,

' of. esteriflcation' and which preferably should be involves impregnating a substantially anhydrous carbohydrate with a substantially anhydrous monohydric aliphatic alcohol or monohydric alcohol and ester containing a halogen oxyacid of relatively high oxygen content, as perchloric acid in the hydrate form, which constitutes a relatively fixed constant boiling acid soluble in the monohydric alcohol, and which is convertible by dehydration into a more or less volatile oxide as chlorine heptoxide which appears to be more effective as an esterification catalyst than the original halogen hydroxy acid, particularly when the same is used in conjunction with a relatively smaller amount of other suitable oxyacid of sulfur or phosphorus.

The mechanics of this invention appear to be that the impregnation of the carbohydrate with alkyl hydroxide or ester or mixtures thereof devoid of water repellant substances improves the uniformity of the wetting of the carbohydrate by water formed by reaction and places it on the same phase of reaction as a suitable substanially anhydrous dehydrating and esterifying reagent, such as an aliphatic acid anhydride, as acetic anhydride, especially when a mixed catalyst of the nature herein disclosed has contacted the carbohydrate as herein set forth,

The anhydride reacts with the hydrous halogen-containing catalyst to form a volatile and more effective catalyst such aschlorine pentoxide or heptoxide; reacts with the alcohol (or less vigorously with an aliphatic oxide) to form water and a diluent of the anhydride used to esterify the alcohol to the corresponding ester; and reacts rapidly and uniformly upon the activated carbohydrate to form an ester, as acetylcellulose.

The catalyst thus formed in situ, or in the nascent state as it were in the carbohydrate is unstable in the presence of an oxidant or oxidizable material such as cellulose, and is stabilized during esterification of the carbohydrate and thereafter removed from the formed ester as by an evaporative step, ation and hence requiring little washing, or other form of purification,

The stabilization of the relatively unstable catalyst is preferably effected by' maintaining air or other source of oxygen in contact therewith, for a portion of the time, or throughout the. esteriflcation phase.

The principle of this invention is intimately associated with relative amounts and distribution of water, and minimum amounts of water in each of the entering components, and in each phase of the treatment of carbohydrate initially until the close of the esterification step.' There should be some moisture present to initiate esterification, after which sufiicient water is obtained by virtue of hydroxyl in the alcohol and the hydroxyl in the carbohydrate incident to acetation orother form of esterification with organic acids or anhydrides or both. The moisture originally present in the carbohydrate-just prior to initiation thereby preventing degenerless than one percent as determined by dehydrating at 105110 C., coupled with the relatively small amount of water in the catalytic body as initially introduced into contact with the cellulose, may supply the water to initiate esterification of the alcohol under the conditions prevailing, and this amount of water is usually deemed sufficient, due to the increased receptivity, and increased uniformity Of receptivity of the carbohydrate for esterification reaction, by virtue of the intimate commingling of catalyst and carbohydrate under the conditions herein set forth. Or, the moisture may be determined in. the various components as by the Fischer volumetric method (see Industrial and Engineering Chemistry, Analytical Section, July 1940, page 392).

Esterification is greatly facilitated, accelerated and rendered more uniform by virtue of the presence of the halogen oxyacid anhydride as chlorine pentoxide, or chlorine heptoxide, C1201, as inducing and continuing esterification under the conditions prevailing, when in conjunction with a relatively minor proportion of sulfur acid or phosphorous acid, as sulfur, or meta-, orthoor pyrophosphoric acids. Such chlorine heptoxide has no apparent injurious effects, especially under the stabilizing action of sulfuric or phosphoric acids, due primarily to its proneness to evaporate an completely volatilize from the treated carbohydrate at the close of the esterification. The

presence therein of the neutral, volatile, cellulose ester diluent in ester form, also modifies and lessens danger of untoward effect upon carbohydrate at the initial point of esterification, and during the esterifying cycle.

The halogen oxyacid anhydride is preferably formed in situ and is preferably effected by the reaction of an esterifying anhydride or of phosphorous pentoxide on a perchloric acid hydrate containing a proportion of moisture, say of 60% to absolute H0104, and about two molecules of water, and which is capable of holding 1-1.5 additional molecules of water.

Such perchloric acid hydrate appears to be stable to light and mechanical shock; is soluble in or miscible with the aliphatic alcohols and esters mentioned herein, and has a relatively low boiling point of around 203 C. It therefore will not vaporize from the cellulose or fabric to any considerable extent under the conditions to which the fabric is treated prior to esterification.

For purposes of description, this invention may be said to involve two steps, both carried out with substantially anhydrous materials as expressed in percentage of the combined reactants, and as follows:

(1) Treatment of carbohydrate prior to esterification with catalyst associated with alkyl hydroxide, with or without alkyl acetate.

(2) Contacting treated carbohydrate with ester-forming components.

1) Preliminary treatment of carbohydrate.- For purposes of illustration only, one exemplification of this process will be described as of treatment of normal cellulose in the fibrous form and in the textile condition, as muslin, linen, duck. weight, weave or weft of suitably purified cellulose fiber.

The catalyst selected is first dissolved or suspended in the proportion desired in the alkyl hydroxide or ester or mixture thereof, or mixture of alkyl hydroxides, with or without the addition of an alkyl ester thereto, all in the substantially anhydrous condition.

. either at room or elevated Synthetic methanol alone or with a proportion of ethyl ether, or "absolute" ethanol, in general has been found preferable, especially when a fibrous carbohydrate carboxylate is to be the finished ester.

Ii upon contact of catalyst with alkyl hydrox; ide, too much heat is evolved as the result, the mixture may be cooled before use or the alkyl hydroxide may be cooled beiore admixture of catalyst therewith. Catalyst in solution or suspension or both, is then contacted with the carbohydrate temperatures, and allowed to remain in contact therewith for a period oi'time, from a few minutes up to several hours or longer, depending in a measure upon the amount and nature of the catalyst employed, and the kind and relative purity of carbohydrate employed.

The composition may be agitated during the preliminary carbohydrate treatment step is desired, and it has been found advisable to limit contact with normal air on account of moisture absorption to an unknown and variable degree.

No esteriiying acid or anhydride or water repellent agent is used in this preliminary carbohydrate treatment step. I

In another variation of the process for esterii'ying cloth according to this invention, an ordinary padding machine may be used to immerse the dehydrated carbohydratein the aliphatic alcohol oraliphatic alcohol and ester in which there has been thoroughly mixed the halogen hydroxy acid as perchloric acid containing a minor proportion of sulfur or phosphorous oxy-acid or respective anhydride. There is no observable reaction between the perchloric acid admixed. with sulfuric acid or phosphoric acid where methanol or equivalent is used, or on cellulose in this treatment, even at the boiling point of methanol.

The methanol uniformly disperses the catalyst throughout and in the interior of the cellulose fibers, and removes, unifies, disperses or equalizes the distribution of the remaining variable amounts of water moisture from the cellulose, but does not seem to remove the water of hydration from the halogen oxyacid used, at least to an observable degree.

Speaking oi normal cotton cellulose, saturation point of the cellulose fibers is about 62% of their weight of methanol and about 1.3-1.6% of their weight of perchloric acid, or 1.4-'1.9% of mixed catalyst, which is selectively not absorbed from the methanol. Such a high methanol content is usually not necessary, and generally is undesirable for esterification, since the amount of methanol carrying catalyst .left in the fibers should normally be only sufflcient to form by reaction with anhydride sufilcient water for initiation of cellulose esterification.

Consequently the saturated cellulose, after having passed through squeeze rolls, is subjected to an evapor'ative step until the methanol'content is reduced by evaporation to between and 30%,

preferably to about 20% to 25%, based on the dry weight of the cellulose.

Or, in a modification of this step, the amount of methanol used may be just suificient to produce the desired amount of methyl ester in the acetation step; and the difference inliquid associated with catalyst in the carbohydrate pretreatment 'step may be a monohydric aliphatic ester, such as methyl acetate. In such case, the step of removal of methyl hydroxide to the degree desired for 'hydroxyl elimination in the subsequent acetation step is unnecessary.

thereby rendered more reactive and more uniformly receptive to subsequent esterification, and the esterification is carried out in a more uniform manner and is less time-consuming, thereby producing a product of relatively high stability and yield.

The catalyst solvent containing hydroxyl in conjunction with the relatively small amount of moisture still normally retained in the cellulose it such moisture there now be, admits of initiation of esterification, and in a manner without observable local rise of temperature, due to this uniform prior dissemination and dispersion to an almost intermolecular degree and actual interpenetration of catalyst uniformly and completely into cellulose substance.

That is, at the moment of commencement of esterification when initiated under the conditions as described herein as prevailing, each cellulosic entity is permeated and saturated in a uniform manner with the same proportions or amount of catalytically-acting body, and the relatively small initially present proportion of moisture is uniiormly disseminated throughout the mass.

This obviates the possibility ofserious localized reactions and an irregular rate of esterification with corresponding formation of a series of different carbohydrate organic acid esters, as cellulose acetates, as determined by varying amount of acetyl associated with the cellulose, such localized reactions being always accompanied by rise in temperature and disintegration and degradation of the cellulose.

It has been discovered, as a generality, that localized and irregular reactions during esteriflcation are due primarily to irregular distribution of water occluded in, or physically or chemically combined with, the cellulose or the esterifying bath components.

-While the presence of water is essential to esterification, especially in its first phases, it has been demonstrated that its action can effectively be controlled primarily if not only by the formation thereof by reaction in situ, and that all of the components present and involved in the esterification oi the cellulose, should collectively be initially so anhydrous that their determinable aggregate water contact is initially insuiilcient to initiate esterification in the treated cellulos or to set up observable local reaction. The preferred practice of this invention therefore, requires exclusion of water to the utmost degree possible from the esterifying substances, and especially the uniform displacement, diffusion and dissemination of minute quantities of extraneous water that may remain. And the development by reaction, of water in situ in the molecular structure of the cellulose is suflicient, once esterification is initiated under these conditions, to continue cellulose esterification uniformly to a product of substantially maximum degree of combination of cellulose with acetyl. Such Water of reaction in contradistinction to small amounts of water originally present in the cellulose or'reactants, is generated by the esterification of the 7 water-soluble aliphatic alcohol or alcohol alone or in the presence of aliphatic oxide, which more readily esterifies than does the cellulose, such esterification producing an ester which is a diluent but a non-solvent of the acetated cellulose upon formation. The preliminary esterification of the alcohol appears to occur, at least in its first phases, immediately prior to, or concurrently with the esterification of the cellulose and in intimate contact with the structure thereof. The much smaller molecular weight of the aliphatic alcohol, or aliphatic alcohol in conjunction with aliphatic oxide, in comparision to the relatively huge cellulosic aggregate, causes initiation of esterification first in the alcohol and releases water to initiate esterification of the carbohydrate and to assist in the continuation of that esterification.

The removal of the practically all free or originally uncombined water, including physically attached or chemically combined water (so-called water of constitution) from the carbohydrate, as cellulose, and the complete and uniform impregnation of its molecular structure with anhydrous aliphatic hydroxide, places the cellulose in the same phase or zone of reaction as the water-free esterifying bath. Even if the esterifying bath originally contained small amounts of water, the probability is that it would first be combined with the acid anhydride to form the corresponding acid.

By thus eliminating any interfacial tension between the constituents of the esterifying bath and the products to be esterified, the latter are completely, uniformly and substantially instantaneously penetrated and impregnated by the former, so that the esterifying reaction proceeds uniformly under these conditions throughout the molecular cellulosic structure.

By thus observing the prior outlined conditions, this permits of substantially instantaneous subsequent esterification perfectly uniform throughout, and hence with no observable appreciable degradation of cellulose in passing from the nor.

mal into the ester form, thereby assuring that the cellulose ester so formed shall retain its original desirable physical characteristics as tensile strength not only substantially unimpaired, but usually appreciably augmented, sometimes up to 50% increase and more.

This includes toughness, elasticity, flexibility, resiliency, tensile strength and uniformity of gelatinization, colloidation and solution in a wide variety of solvents, solvent combinations, diluents, flexilizers, plasticizers and supple-inducing bodies.

Such acetated celluloses in the fabric form possess the desirable qualities to a much greater degree than do yarns and fabrics made from or containing hydrolyzed, degenerated or oxidized cellulose, either before or after esterification thereof.

The esterification of celluloses according to this invention, especially after the cellulose filaments have been spun into yarn or woven into fabric, results in an increase in diameter of the individual filament, an increase in number of turns or twists per inch in the yarn, and the relative transparency, translucency, opacity, luster and other properties of such acetated yarns or fabric made therefrom, may be largely modified and controlled by the degree of tension applied thereto in one or more directions during the esterification and subsequent treatments and usually until the finished fabric has assumed the air-dry condition,

The. weight of the carbohydrate is also increased incident to acetation by this invention, up to 50%, and even more.

After contact of catalyst and cellulose in the presence of an aliphatic hydroxide or oxide or mixture thereof, or a body possessing alcoholic functions, for the length of time required to assure complete and uniform association and permeation of catalyst of the nature as herein disclosed with and into the cellulose, either at rest or with agitation, excess of liquid and catalyst is removed in any convenient manner, as by pressure, centrifugalization or evaporation, and until the original cellulose shows a gain in weight of not to exceed about 30%, when it is immediately,

or after maturing, contacted with esterifying esterifying bath should contain a proportion of inert diluent or carbohydrate ester non-solvent, which non-solvent for purposes of economy and subsequent recovery may be the same ester as that formed by introduction of the alcohol in the prior pretreatment step, after that alcohol or ether is subjected to esterification.

If acetation of cellulose is desired and ethanol has been used as the vehicle to contact cellulose and catalyst, then the esterifying bath is preferably composed of or contains the aliphatic acid anhydride as acetic anhydride, with ethyl acetate as non-solvent or diluent for the acetated cellulose formed.

If the ethanol above has been replaced by a mixture of ethanol and ethyl acetate or methanol and methyl acetate then the esterifying bath diluent may be either methyl acetate, ethyl acetate, or a mixture of the same in the desired proportions,

If the process is to be a more or less continuous one as where rolls of textiles are to be esterified, then the textile is preferably placed under tension, either or both longitudinal or lateral, the degree of tension employed in either or both directions being determined by the properties desired in the esterified textile. Cotton or linen textile, or a mixture of mercerized and non-mercerized cotton fibers, undergo considerable contraction upon being esterified in accordance with this invention.

The stresses on the textile are preferably gradually decreased during the early stages of esterification and gradually increased during the later stages of esterification by varying the tension applied to the textile.

Where relatively considerable tension is employed in either one or both directions, it has been found that certain physical properties as luster are profoundly modified, esterification proceeding more speedily and uniformly when considerable tension is applied to the fabric, perhaps due to more ready penetration in the textile of esterifying agent in the stretched condition.

Esterification of carbohydrates, particularly cellulose and readily noticeable in the fabric form, causes a distinct tautening and contraction, and variation in tension or degree of tension imposed during th esterifying step, proalcohol and cellulose,

duces corresponding results in appearance of the finished product, especially in augmentation of the sheen, feel and facility of penetration of dyestuif and other treating materials normally applied to cellulose goods.

After contact of esterifying liquid with cellulose for the period required to produce the degree of esteriflcation desired, and preferably in the presence of a source of oxygen, fabric is removed from the zone of further esterification, reactants removed therefrom as by washing or a solvent recovery step, and the fabric freed from excess moisture, as bypassing through a dryer, still under tension, or the tension may be partially or wholly removed therefrom.

In lieu of acetic anhydride, other esterifying anhydrides or anhydrous fatty acids maybe used, as formic acid, propionic acid, propionic anhydride, or mixtures thereof, where a mixed carbohydrate ester is to be produced.

This method permits the use of amounts of esterifying acids or anhydrides in such slight excess of the amounts theoretically required for reaction with the alcohol and with the cellulose, that uniform mono-, diand trl-esters of cellulose, broadly speaking, may be directly produced by properly proportioning the amount of the esterifying anhydride or acid or both, to the and control of the temperature and other constants during esterification, thereby avoiding or minimizing necessity for hydrolyzing or saponifying the primary ester to secondary ester, unless so desired.

Factors governing the percentages of acetic anhydride usually necessary for the formation of a desired primary or secondary cellulose acetate, the reactions involved, and controls desirable in commercial practice are illustrated by the following'table applicable to the introduction into acetic anhydride of 100 pounds of cellulose containing 30% menthanol and catalyst as herein before set forth:-

Pounds of water formed 8.46 Pounds of methyl acetate formed 69.3 Pounds of 100% acetic anhydride hydrolyzed by the water formed 48.0 Pounds of acetic acid formed from the hydrolysis of the acetic anhydride 56.4

To form a cellulose triacetate (based on a Ca cellulose molecule) under such conditions, there theoretically should be initially present not less than 293 pounds of acetic anhydride; or to form cellulose diacetate ther should be initially present not less than 227.3 pounds of acetic anhydride; or to form cellulose monoacetate there should be initially present not less than 161.6

pounds of acetic anhydride.

In commercial practice of this inventionit is advantageous to use approximately or more in excess of the amounts of acetic anhydride theoretically indicated, but this amount is sus-' ceptible to considerable variation depending upon the condition and nature of the carbohydrate at the time of esterification, temperature of esterification, and the particular halogen hydroxy acid with sulfur or phosphorous oxyacid used as catalyst.

The uniform saturation of fibers with such small amounts of anhydride is difficult, hence it is generally desirable to add to the anhydride a sufficient quantity of diluent to initiate, facilitate, control and unify reaction. When the cellulose is simply passed through the esteriflcation bath and the reaction completed during acetate being formed, as for instance, acetic acid 1 may be used as diluent when cellulose acetate in solution in the esterizing bath is desired, or a polyhydric alcohol may be used as the hydroxide for bringing the catalyst in contact with the cellulose. As example, if a dihydric alcohol as glycol, or a trihydric alcohol as glycerol be employed, the acetated glycol or acetated glycerol.

formed in the acetating bath has solvent effect upon the carbohydrate ester formed.

Example I.- -Acetation of linters. As a quantitative illustration of one method of carrying this invention into effect and as applied to cellulose as the carbohydrate in the non-woven condition, the cellulose -as linters properly purified, is rendered bone dry orslightly drier by removal of moisture therefrom and until the moisture content is preferably below 1%. allowed to cool, and kept in a dry atmosphere until used.

To parts of such cellulose is added a mixture of l.5-1.'75% of perchloric acid of 70% to 75% strength, and 0.5% sulfuric acid of about 66 B. strength, dissolved in or admixed with anhydrous methyl alcohol, at least equal in weight to the weight of the cellulose to be treated.

The addition oi'dissolved catalyst is made to cellulose at normal or elevated temperature, and the mass stirred or otherwise agitated for from a few minutes to several hours. Contact of cellulose and catalyst is maintained preferably in a closed container to prevent or minimize absorption of atmospheric moisture, unless the atmosphere has been dehumidified.

The cellulose and catalyst may be allowed to remain at rest for a further period if desired, to ensure maximum reactivity to be imparted to the cellulose.

At the close of this steeping, maturing, activation or intermingiing step, the cellulose is then reduced in alcohol content to 20% to 30% increase in weight of the cellulose, preferably about 25% by weight, by a pressure, evaporative or centrifugal operation, and then immersed in a bath containing about 400 parts concentrated acetic anhydride, and the mixture agitated, preferably at not to exceed 35 C., action being continued until an apparently homogeneous product results, and substantially no unacted upon fibers are visible under low power magnification. If the. acetating mixture is too viscous, it may be thinned with a cellulose acetate solvent as acetic acid.

During acetation, oxygen in the form of a plurality of small streams of air may-be contacted with ester esterifiant, as by bubbling air or other source containing oxygen passed in contact with or through the acetating mixture.

The glutinous mixture may then be stored to homogenize or ripen for a period, or may be immediately precipitated by contact with cold water if the substantially triacetate form is de-' hours,

case the acetated cellulose is freed from reactants by precipitation or by solvent recovery, usually by both in manufacturing operations, and dried at a moderate temperature.

It has been found that when operating as above and using sulfuric acid in conjunction with a halogen oxy-acid as perchloric acid as catalyst, there is no detectable sulfonic or other sulfur-containing compounds present in the finished cellulose acetate, and hence stability on long storage is not diminished to any considerable degree as is usually the case when sulfuric acid is used alone as a catalyst in cellulose acetation.

Methyl acetate is not as desirable diluent for acetic anhydride in cellulose esterification where sulfuric acid is used in notable quantities as cellulose catalyst, an aromatic hydrocarbon as benzene, toluene or xylene being more suitable as diluent where fibrous cellulose acetate is to be produced, used either alone or in conjunction with an alkyl ester of a monocarboxylic aliphatic ester.

With the use of acids of phosphorus inconjunction with a high oxygen content halogen oxy-acid as catalyst, ortho-phosphoric acid (H3PO4) is most readily available either as in the solid or syrupy form, or as the anhydride, phosphorus pentoxide. Insofar as the deportment herein is concerned, metaphosphoric acid (HPOa) may be regarded as a partial anhydride of orthophosphoric acid, and pyrophosphoric acid (H4P2O7) likewise as a partial anhydride f orthophosphoric acid, according to the reaction The relatively small amounts of phosphoric acid employed do not diminish the stability of the esteri'zed carbohydrate, insofar as has been determined.

EramiOZeIL-Acetation of starch. One hundred parts of purified starch of commerce is deprived of substantially all moisture, and wetted with a mixture containing 2 to 2.25% by weight of 70% to 75% perchloric acid and 0.5% orthophosphoric acid or 0.3% metaphosphoric acid, in a mixture of 150 parts anhydrous methanol and 50 parts absolute ethanol, and the mixture stirred repeatedly up to a maximum period of about 4 temperature not being allowed to rise above about 30 and preferably not above 25 C.

The mass is then reduced in weight by pressure to about 125 parts, broken up into a. fine powder, and immersed in a mixture of about 300 parts concentrated acetic anhydride and about 300400 parts anhydrous methyl acetate, or methyl acetate containing about one-third ethyl acetate, agitation being continued during addition of acetating mixture, and continued at temperature preferably not to exceed 25 C. until a sample withdrawn shows a solubility in alcohol-free chloroform, or other solubility characteristics depending upon the degree of acetylation desired.

The granular mass, still substantially conserving' the morphological structure of the original starch, is then washed in water to neutral reaction, centrifugalized and dried at a comparatively low temperature.

Example III-Acetation of cellulose in tea:-

. tile 'form. One hundred parts by weight of a thin muslin of width and length desired is deprived of moisture until it is substantially anhydrous, and then uniformly impregnated in the cooled condition with a mixture of 100-200 parts anhydrous methanol containing dissolved therein 1.5 to 2% by weight of 70-75% perchloric acid, 0.2% sulfuric acid and 0.2% orthophosphoric acid for a 12 period of about 5 hours, the cloth being turned or otherwise agitated frequently during the contacting period of catalyst with cellulose.

The preferable amount of methanol to use, and the treatment period of cloth with dissolved perchloric-sulfuric-phosphoric acid catalyst will depend in a measure upon the weight, texture, weave and other physical characteristics, and the nature of the cloth being treated.

At the expiration of the impregnation or disseminaticn period, the cloth is placed under pressure or liquid evaporated therefrom until the weight of the cloth has been reduced to under of its original weight, when it is then placed under uniform or variable tension and immersed in a closed container containing 300-350 parts concentrated acetic anhydride and 50-200 parts methyl acetate, the temperature range being kept below about 25 0. Or the cloth may be placed under tension during the period of contact of catalyst with cellulose.

When a sample of cloth removed and purified shows the physical characteristics of "cellulose triacetate (maximum acetated normal cellulose or thereabouts) the cloth, still under tension, is treated to remove reactants in any suitable manner, and moisture removed therefrom, after which the tension is removed.

In addition to the application of tension during cellulose treatment, physical characteristics as luster may also be modified by passing the acetated cloth into or through a chamber containing volatile solvents, plasticizers or other modifying liquids or solids in vapor form, whereby a degree of incipient gelatinization of the acetated fibers is allowed to take place, in degree depending upon the effect desired, and being modified by the tautness of the fibers during said treatment.

In a modification of the process, also given for illustrative purposes only and with the understanding that the reactants and conditions may' preciable oxidation or decomposition of the cellulose.

When the moisture content of the fabric has been reduced below 1%, the dehydrated fabric, preferably after being allowed to cool, is passed through a bath comprising sufiicient anhydrous methanol containing mixed catalyst to thorough- 1y impregnate the fabric. After a sumcient period of contact between catalyst and fabric, liquid is removed by passage of the fabric between squeeze rolls, and the methanol content then further reduced substantially below its saturation point by passing the fabric through a further drier section, preferably so adjusted as to temperature and length that a single passage of fabric therethrough reduces the methanol content in the fabric to between 10% and 30% and preferably 20% to 25% increase in the weight of the goods, and the acid content is approximately 1 /2 to 2% of the weight of the goods. While this impregnation to a satisfactory degree of cellulose with as those which are set or 13 catalyst is normally but a matter of a few minutes, yetmore uniform results appear to be obtained where cellulose and catalyst are allowed to contact several hours before esterificationis initiated.

The evaporated methanol may be recovered from the drier and condensed.

The fabric is cooled by evaporation of methanol therefrom and is then fed through a solution containing 100 parts concentrated acetic anhydride to 50 parts methyl acetate. It is then passed under tension over rollers in contact with a stream of air.

The acetylation is completed in air and the catalyst or its decomposition products removed from the acetated fiber as by evaporation followed by washing, usually in less than a half hour. The temperature of the bath does not require external thermal control as the rise in temperature is insufi'lcient to degenerate the cellulose, and when the bath contains diluent equal to more than the weight of anhydride, the temperaturerise of the bath is negligible.

The fabric is then fed into a washer to eliminate traces of non-volatile catalyst and washed in water, preferably exceeding the esterification temperature. Ordinarily any residual reagents may be completely washed out within minutes with water at a temperature of 15 to 25 C. The product is then in suitable condition for finishing as a textile fabric.

If it is desired to further waterproof the fabric,,it may be passed through a confined atmosphere containing a solvent for the cellulose acetate, or a solvent or cellulose ester or ether lacquer may be uniformly sprayed thereon, then passed through a heating chamber for solvent removal. This induces an incipient gelatinization of the exterior layers of acetated cellulose fabric to a varying degree, and more or less binds thefibers together by the agglutinating action of the dissolved or softened acetate portion, or

by the lacquer solution.

This invention permits the formation of yarn or textiles of various and contrasting colors or at a temperature not much shades of dyeing or printing the cellulose fibers,

yarns or fabrics with ordinary cotton dyes which are'unaifected by the steps in this invention (such developed, as by acids), prior to esterification thereof, thereby eliminating or minimizing the need of special and expensive dyes ordinarily required for dyeing carbohydrate esters, especially organic esters of cellulose. In'the formation of textiles by weaving artificial cellulose acetate filaments by extrusion of solution through minute orifices into a liquid precipitant or into an evaporative atmosphere, there are normally formed many broken filaments constituting fuzz on the textile which materially diminishes its quality unless removed. By submitting the cellulose textile to a gassing step followed by brushing, such outwardly projecting short fiber filaments are removed prior to transformation of cellulose into cellulose ester.

Cellulose acetylated to a tri-acetate or di-acetate as herein described, or the usual commercial cellulose di-acetate fabric wovenffrom extruded filaments, may be deacetylated for the production of novel soft, crease-resisting and lustrous fabrics by treatment with a suitable deacetylating agent, such, for example, as an anhydrous alcohol containing small amounts of alkali metal hydroxide or alkali earth metal hydroxide, as sodium hydroxide, potassium h 14 droxide, barium hydroxide or strontium hydroxide dissolved therein and subsequent removal of reactants, or in other manner.

The reagent employed for the removal of acid radicals from such acetylcellulose must be water soluble, but there must be no water present when it is introduced into the cellulose, as it is desired that the reaction take place when the cellulose is removed from the alcohol bath and introduced into water.

As an example of a treatment for the removal of acetyl radicals from acetylcellulose, 1%-5% by weight of potassium hydroxide may be dissolved in methanol and the acetylcellulose immersed therein. After immersion of the cellulose ester in the alcohol for about twenty minutes a gradual change in transparency begins to a pear and at the end of an hour or so the acetylcellulose seems to reach its maximum transparency. Upon removing the same from the alcohol and introducing it into warm water, the fabric becomes limp. After removal from the warm water, an ordinary wash in cold water and an ironing out, there remains a limp, soft, lustrous piece of cotton cellulose which is not soluble in chloroform, acetone, or other suitable neutral volatile organic solvent, which is resistant to creasing and which maintains substantially the normal strength of the original cotton piece goods from which prepared. An application Serial No. 351,912 relating to the art of esterification is co-pending.

What is claimed is:

1. Process for esterifying carbohydrate com prising impregnating said carbohydrate with oxy-- acid of a halogen of greater atomic weight than fluorine in association with oxyacid selected from the group consisting of oxyacids of sulphur and phosphorus, all acids relatively high in oxygen content in presence of an anhydrous monohydric alcohol, removing a portion of the liquid, then submitting said carbohydrate to esterification with a lower fatty acid anhydride of the acid to form the carbohydrate ester.

2. Method of acetylating comprising drying purified carbohydrate until water content therein is less than one percent, impregnating said carbohydrate with anhydrous methanol containing no more than 2% perchloric acid and no more than 1% phosphoric acid dissolved therein, allowing contact of acid with carbohydrate until absolute penetration has taken place, removing a portion of the liquid portion, then treating the moistened cellulose with a lower fatty acid acetylating agent free from acetic acid.

ANNETTE HARRIS PRA'I'I, Administratria: of the Estate of William Beach Pratt, Deceased.

REFERENCES CITED The following'references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,018 Ruperti Dec. 21, 1937 2,221,184 7 Ellis Nov. 12, 1940 2,170,024 Heckert Aug. 22, 1939 2,130,150 Nathanson Sept. 3, 1923 2,127,586 Dreyfus Aug. 23, 1938 2,069,971 Schneider Feb. 9, 1937 2,000,602 Malm et al. May 7, 1935 2,076,555 Futhergill Apr. 13, 1937 1,739,863 Rosenthal et al Dec. 17, 1929 2,053,767 Dreyfus Sept. 8, 1936 (Other references on following page) Number Malm et a1. July 13, 1937 Number Number Name- Date Seymour et a1 June 11, 1940 Cross et ll May 4, 1909 Jaeger July 24, 1928 Muller et a1. Dec. 21, 1937 FOREIGN PATENTS Country Date Great Britain Feb. 13, 1930 Great Britain Feb. 15, 1934 Great Britain Aug. 26, 1940 

